SSP Pod Approved
For Service

After more than two years of development and successful performance trials at Howaldswerke-Deutsche Werft AG in Kiel, the Siemens-Schottel Propulsor (SSP) consortium was granted approval for the new SSP marine propulsion system. Classification society Det Norske Veritas was responsible for technical acceptance of the propulsion system for worldwide service.

The SSP is the result of a successful cooperation between two German marine industry stalwarts, Siemens Marine Engineering Subdivision and Messrs Schottel of Spay. Work began in 1997 on the development of a marine propulsion "pod" system that would be offering not only economic advantages, but superior technological performance. The pod-type propulsion system features an electric motor housed in a pod or nacelle suspended beneath the hull of a vessel, and providing direct drive to a propeller of propellers. The fact that the pod can be rotated about its vertical axis too, so that it points in any required direction, means that the system also performs a steering function.

The power output of the unit tested at the shipyard amounts to 7MW, which corresponds to 9,510 hp.

Similar type pod systems have already been adopted for technically advanced uses, and have been specified and operational aboard such high value vessels such as cruise ships. The system is particularly interesting for the cruise ship market because its twin screws produce low noise and vibration levels to ensure passenger comfort.

Siemens, one of the world's foremost suppliers of electric marine propulsion systems, provided a permanent-magnet motor, which has permanent magnets attached to the rotating rotor. The design of the permanent-magnet motor has been undergoing development and testing for the past 12 years and is now ready for general use, including by the Germany Navy. The Propulsor employs the patented "Twin Propeller System" developed by Schottel GmbH. The prinappreciably through changes in speed and course.

It is noticeable that in the North Atlantic, mainly smaller vessels of about 591 ft. (180 m) in length are affected, whereas in the North Pacific it is more so the larger ships. This observation by the Salvage Association is confirmed by the results of a research project conducted by Germanischer Lloyd, in which inter alia the waveinduced loads and bending moments on various container carriers were measured. Similar problems have also occurred on modern cruise liners, where a projecting bow is intended to give the ship the looks of an elegant yacht.

A significant advantage for passenger ships is, however, that the bridge is situated far forward, and the master is thus much closer to the bow action than in a jumbo containership. Nonetheless, there is also in the passenger/ferry ship segment a strong trend towards fast ships: at present, four jumbo ferries and two fast cruise liners are under construction to GL class, all with service speeds of around 28 knots. GL immediately took appropriate action as a result of these findings, and initiated a research project in which, amongst other factors, extreme loads on the forebodies of large and fast ships are being investigated. The development of fast RoRo passenger ferries is the reason why a conventional but very fast (28 knots) RoRo passenger ferry was chosen as the reference ship for the new EU research project DEXTREMEL. In this project, the extreme loads on the ships are being investigated in depth, with the loads on the forebody representing one of the main aspects. Another work package involves determining the structural reserve strength for the elements of a damaged structure and, associated with this, an investigation of the possibilities for enlarging this residual structural strength without increasing the steel weight appreciably. In these studies, peak pressures cased by slamming are being calculated for a variety of bow shapes using modern methods such as computational fluid dynamics. Naturally, the results obtained from the example of a fast RoRo passenger ferry can be transferred fully to other ship types including the container carriers mentioned. The initial results have already been incorporated into the new edition of the Construction Rules for Hull Structures (Edition 1998). The new regulations include increased design pressures for the forebody structure, including the forecastle, together with structural requirements and guidelines on increasing the ultimate strength under extreme loads. The consideration of stresses caused by hydrodynamic impact forces on the forebody, as part of the global analyses of the large containerships, is the current state-of-the-art ship structural analysis at Germanischer Lloyd.

Just how urgent these amendment to the Rules are with a view to improving the operational safety of modern containerships can be seen from the fact that responsible-minded shipowners - after having been informed by GL - have already, before official publication, made them a contractual requirement for their order of Panamax as well as post-Panamax vessels.